An oximeter senses signals that can be used to determine blood oxygenation, or oxygen saturation of blood of a patient. One oximeter has included an emitter and sensor. The emitter emits electromagnetic radiation (commonly referred to as light) in the visible and the near infrared regions of the electromagnetic spectrum, and the sensor senses red and/or infrared light and generates signals indicative of the sensed light.
With a transmission-based oximeter, the emitter and the sensor are located opposite each other across an examination region, and the emitter emits light that traverses vascular or interstitial tissue of anatomy (e.g., a finger, an earlobe, etc.) located in the examination region and is sensed by the sensor. With a reflectance-based oximeter, the emitter and the sensor are located on the same side of the examination region, and the sensor senses light emitted by the emitter that reflects from the vascular tissue.
The sensed signals are used as inputs to algorithms, which are used to determine oxygen absorbance values. Generally, at known selected wavelengths of light, oxygenated hemoglobin absorbs more infrared light than red light, and deoxygenated hemoglobin absorbs more red light than infrared light. Algorithms compute a ratio of the absorbance of red light to the absorbance of infrared light and that is then used as an estimate of the percentage of the hemoglobin that is bound with oxygen, which is used to estimate the oxygen saturation of the blood.
Another device uses near infrared spectroscopy (NIRS) to determine tissue oxygenation in interstitial fluids within the examination region.
The above-noted devices have employed a compact light emitting diode (LED) integrated chip (IC) mounted on a sensor assembly or rigid light bundles mounted to the assembly. Unfortunately, the sensor assembly can be relatively costly, and the rigid light bundles can be cumbersome. In addition, the above-noted devices use custom algorithms, whose computations depend on the precise absorbance at a number of light wavelengths, and precise angles of detection, all of which dictate the precise location of the LED IC on the assembly.